Koalas Research Paper

Hannah Cho

Honors Biology

Mr. Jeffery

16 April 2017

Evolution of Koalas

Koalas are one of the things that a person would think of when they hear Australia. Most people call them koala “bears” but this is a common misnomer. Koalas are more closely related to kangaroos and wombats than bears. Their scientific name is Phascolarctos cinereus. They have evolved and adapted to their environment for survival. Their lifestyle of eating and sleeping, which people think is amusing, is actually a result of their adaptation to the environment. Koalas have physically evolved in various ways to adapt to the environment.

The diet of the koala is one aspect that shows that they have adapted to their environment. The main diet of the koala is eucalyptus

leaves. Koalas are the only mammal, other than the Greater Glider and Ringtail Possum, that can eat these leaves. The eucalyptus leaves are known to be highly toxic to other mammals. The digestive system of koalas evolved to detoxify the poison in eucalyptus leaves. Due to their unique diet, koalas have one the largest digesting systems. The food that a koala consumes goes through their stomach to their small intestines and to the hindgut. Caecum, one of the chambers of the hindgut is a critical digesting organ that the koala has. This organ breaks down the high-fiber eucalyptus leaves and makes them easier to absorb. It is also where koalas detoxify the leaves. Along with their diet, koalas are also well-known for their long period of sleep. This is because of their slow metabolism rate. The slow metabolism of koalas allow them to retain food in their hindgut for over 100 hours. Koalas retain food to extract as much energy and sleep 18-20 hours a day to minimize the amount of energy used.
Along with digestion, the teeth of koalas is another example of its evolutionary adaptation. In order to break down eucalyptus leaves, strong teeth is needed. The front teeth of koalas that are sharp tear the leaves and the back teeth that are relatively flat grind the leaves before swallowing them. A recent study conducted by a team led by Dr. Jullien Louys proved that the teeth of koalas was a feature that has evolved. According to the study, the chewing apparatus of koalas is advanced than the Litokoala and Nimiokoala which are fossils of extinct koalas. This is because at the time the Litokoala and Nimiokoala lived, the Australian continent had fairly moisturized plants. However, as the continent dried “the flora became dominated by plants with hard, tough leaves, [and] animals such as koalas had to adapt to this new food resource” (Society of Vertebrate Paleontology).
Aside from adaptations to its diet, koalas have also evolved physical features to adapt to the environment.

One example is the unique shape of a koala’s hands.The front paw of a koala looks fairly similar to a human’s hand. However, it has two thumbs and three fingers. Their hind paws are different from the front paws. The second and third digits of their hind paws are fused together and they have one thumb. They have sharp claws on both paws that help them have a good grip on trees. The rough skin on their palms is another factor that assists them when climbing the tree. By taking a closer look at the hands of koalas, one can see another piece of evidence for evolution. The fingerprints of koalas are very similar to those of humans. This is an example of convergent evolution. Scientists believe that both human and koalas have fingerprints because they both need the ability to grasp on objects. Fingerprints give control when grasping something. Although ancestors of koalas and human have branched apart about 70 million years ago, the two species have developed fingerprints for a similar

function.
Another physical feature of koalas that indicate that they have adapted to the environment is their facial structure. Koalas have a large nose and ear but small eyes. They depend on their sense of smell and hearing to survive. Their sense of smell allows them to smell the different levels of toxin in eucalyptus leaves. Due to their selective appetite, koalas only eat a few of about 600 species of eucalyptus trees. Their good sense of smell has evolved to adapt to its habitat where it has to find and eat specific leaves. Also, they can smell scent warnings put by other koalas. Scientists think that the koalas are born with a good sense of smell. Newborn koalas move to the pouch of the mother using their sense of smell to sense the mother’s milk. Big ears of a koala is another feature that is unique. The sense of hearing is needed for communication. Compared to their nose and ears, the eye is small because it is not as important in survival to koalas.
One unique physical structure of koalas that people do not know about is their tail. The tail is usually not visible to a human’s eye but it is present in the skeletal structure. Their tail is a vestigial feature that was inherited from evolutionary ancestors but does not have a function. This indicates that it once had an external tail but evolved to have a shorter tail that is no longer visible because the structure was not used.
The dense and wool-like fur of koalas is another example of an adaptation.

The color of the fur varies depending on the location of the its habitat. Generally, koalas living in the South have fur that is darker than those living in the North. The fur protects the koalas helps maintain its temperature from cold and hot weathers. It also acts as a raincoat and repels water. In cold weathers, the fur acts as a great insulator and protects koalas from losing too much energy (calories) fighting the cold. Furthermore, in hot weathers, the fur protects koalas from losing water in their body. Regarding a koala’s posture and habitat, it has a denser fur on its rump that is consisted with tougher connective tissues. The thick fur acts as a cushion for its bottom when sitting on a tree. The fur of koalas keep their body temperature stable and provides a cushion for its usual posture sitting on a

tree.
As mentioned in previous paragraphs, Koalas have adapted to the environment in many ways. Their struggle to survive in their environment is shown by these factors. Unfortunately, people are harming their environment and habitat. People are clearing eucalypt forests for agriculture, factories, or housing. This takes away their habitat and main source of food away. Also, as more and more people move and live closer to the koala habitat, it is threatening the koala population. Furthermore, arising carbon dioxide levels is harming their main source of food, eucalypt trees. The nutrition and toxic level of these trees are affected by carbon dioxide. If carbon levels in our atmosphere continue to rise due to pollution koalas will not be able to gain the right amount of nutrition and could possibly die from excessive levels of toxic that they are not used to. The people’s effort to live a better life is harming koalas who have also struggled and adapted to their current environment.
It is important to keep koalas safe from such factors because although koalas are not considered as a major component of the ecocycle, it still affects its environmental system. One species that the koalas has a big effect on is eucalypt trees because it is their main diet and they are one of the few animals that eats it. Koalas are keeping the population of eucalypt trees stable. If koalas eat all the leaves of the tree, which is where the tree does photosynthesis, the tree eventually dies. If there are more koalas than eucalypt trees available and the trees cannot reproduce at the rate of its consumption, the koala population would decrease and as the population decreases eucalypt leaves would recover and increase. This allows both populations to be stable. Without koalas the population of eucalypt trees would grow excessively. Stabilizing the population of eucalypt leaves is one short-term effect koalas have in its ecosystem. Furthermore, an increase of eucalypt leaves could lead to a long-term effect. Eucalypt leaves absorb lots of water. If the number of eucalypt trees grows excessively due to the absence of koalas, it could affect the groundwater level and thus other species living around the forest. Koalas are not only stabilizing the population of eucalypt trees but is also protecting the species living around eucalypt forests. On the other hand, koalas are disrupting the ecosystem of certain islands. On Kangaroo Island located in South Australia koalas have thrived without predators. The population of koalas have increased and is threatening the species of mamma gum and thus the birds on the island that rely on mamma gum. Another short term effect of koalas is that they are the prey of dingos and other wild birds in Australia. Although predators of koalas do not entirely rely on koalas, koalas take up a part in their diet. If koalas go extinct, the food web of Australian animals would change.
Koalas have evolved and adapted to their environment in numerous ways. Their teeth and digestive system has adapted to their main diet, eucalyptus leaves. Their hands have evolved to effectively grasp on trees and gain food. Also, their facial structure has evolved depending on which abilities they need the most to survive and their fur evolved to adapt to their climate. Despite their adaptations and struggle to survive, the population of koalas have declined and are in danger of extinction. Majority of these threats are caused by people. Although people may think that koalas are not a key component of the environmental system, koalas have short-term and long-term effects on the ecosystem along with species around them.